<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>输入圆的半径计算面积和周长</title>
</head>

<body>

    <div>圆的半径：<input id="r" type="text"></div>
    <div>圆的周长：<input id="cir" type="text"></div>
    <div>圆的面积：<input id="area" type="text"></div>

    <script>
        var r = prompt('请输入圆的半径');
        if (!isNaN(r)) {
            var cir = 2 * Math.PI * r;
            var area = Math.PI * r * r;
            document.getElementById('r').value = r;
            document.getElementById('cir').value = cir.toFixed(2);
            document.getElementById('area').value = area.toFixed(2);
        } else {
            alert('请输入正确的数字');
        }
    </script>
</body>

</html>